Hi all, I hope your day is going well. I have a 2009 Impala LT trim, 3.5L engine. For a while, it has been leaking coolant, but we didn't know where from. The water pump, thermostat, radiator hoses have all been replaced. Radiator is in good condition. We do not think there is a crack in it or in the reservoir tank. However, after adding coolant to the tank, it will leak out, depending on the temperature and climate outside. What we have noticed is we do see saturation around the drain plug/o-ring, and we do see where it's leaking from under the car, but it seems like a cap or screw is missing from under it, and it leaks a ton there. Any possible fix? I'm tired of scattering around trying to find answers, haha! Here is a pic below, and please help when possible. Thanks.